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1. INTRODUCTION
1.1 Overview
This Guide is designed to assist anyone in the UK who is planning to develop a small-scale hydro-electric
scheme. It has been prepared by the British Hydropower Association in order to support and encourage
new developments in this sector.
The term used in this Guide will be “Mini-hydro”, which can apply to sites ranging from a tiny scheme to
electrify a single home, to a few hundred kilowatts for selling into the National Grid.
The Guide will explain:
• The basic concept of generating power from water
• The purpose of different components of a scheme
• The principle steps in developing a project
• The technology involved
• Where to go for help and sources of funding
The Guide is also available as an interactive web-site, where you can pick out the topics of interest from
the drop-down menus, on:
http://www.british-hydro.org/mini-hydro
1.2 Why mini-hydro ?
Small-scale hydropower is one of the most cost-effective
and reliable energy technologies to be considered for
providing clean electricity generation.
In particular, the key advantages that small hydro has over
wind, wave and solar power are:
• A high efficiency (70 - 90%), by far the best of all
energy technologies.
• A high capacity factor (typically >50%), compared
with 10% for solar and 30% for wind
• A high level of predictability, varying with annual
rainfall patterns
• Slow rate of change; the output power varies only
gradually from day to day (not from minute to minute).
• A good correlation with demand i.e. output is
maximum in winter
• It is a long-lasting and robust technology; systems can
readily be engineered to last for 50 years or more.
It is also environmentally benign. Small hydro is in most
cases “run-of-river”; in other words any dam or barrage is
quite small, usually just a weir, and little or no water is
stored. Therefore run-of-river installations do not have the
same kinds of adverse effect on the local environment as
large-scale hydro.

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2. HYDROPOWER BASICS
2.1 Head and Flow
Hydraulic power can be captured wherever a flow of water falls from a higher level to a lower level. This
may occur where a stream runs down a hillside, or a river passes over a waterfall or man-made weir, or
where a reservoir discharges water back into the main river.
The vertical fall of the water, known as the “head”, is essential for hydropower generation; fast-flowing
water on its own does not contain sufficient energy for useful power production except on a very large
scale, such as offshore marine currents. Hence two quantities are required: a Flow Rate of water Q, and a
Head H. It is generally better to have more head than more flow, since this keeps the equipment smaller.
The Gross Head (H) is the maximum available vertical fall in the
water, from the upstream level to the downstream level. The actual
head seen by a turbine will be slightly less than the gross head due
to losses incurred when transferring the water into and away from
the machine. This reduced head is known as the Net Head.
Sites where the gross head is less than 10 m would normally be
classed as “low head”. From 10-50 m would typically be called
“medium head”. Above 50 m would be classed as “high head”.
The Flow Rate (Q) in the river, is the volume of water passing per
second, measured in m3
/sec. For small schemes, the flow rate may
also be expressed in litres/second where 1000 litres/sec is equal to 1
m3
/sec.
2.2 Power and Energy
Energy is an amount of work done, or a capacity to do work, measured in Joules. Electricity is a form
of energy, but is generally expressed in its own units of kilowatt-hours (kWh) where 1 kWh = 3,600,000
Joules and is the electricity supplied by 1 kW working for 1 hour.
Power is the energy converted per second, i.e. the rate of work being done, measured in watts (where 1
watt = 1 Joule/sec. and 1 kilowatt = 1000 watts).
Hydro-turbines convert water pressure into mechanical shaft power, which can be used to drive an
electricity generator, or other machinery. The power available is proportional to the product of head and
flow rate. The general formula for any hydro system’s power output is:
P = η ρ g Q H
Where:
• P is the mechanical power produced at the turbine shaft (Watts),
• η is the hydraulic efficiency of the turbine, ρ is the density of water (1000 kg/m3
),
• g is the acceleration due to gravity (9.81 m/s2
),
• Q is the volume flow rate passing through the turbine (m3
/s),
• H is the effective pressure head of water across the turbine (m).
The best turbines can have hydraulic efficiencies in the range 80 to over 90% (higher than all other prime
movers), although this will reduce with size. Micro-hydro systems (<100kW) tend to be 60 to 80%
efficient.

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If we take 70% as a typical water-to-wire efficiency for the whole system, then the above equation
simplifies to:
P (kW) = 7 × Q (m3
/s) × H (m)
2.3 Main elements of a scheme
The main figure illustrates a typical small hydro scheme on a medium or high head. Other possible
layouts are discussed in Section 2.4.
The scheme can be summarised as follows:
• Water is taken from the river by diverting it through an intake at a weir.
• In medium or high-head installations water may first be carried horizontally to the forebay tank by a
small canal or ‘leat’.
• Before descending to the turbine, the water passes through a settling tank or ‘forebay’ in which the
water is slowed down sufficiently for suspended particles to settle out.
• The forebay is usually protected by a rack of metal bars (a trash rack) which filters out water-borne
debris.
• A pressure pipe, or ‘penstock’, conveys the water from the forebay to the turbine, which is enclosed
in the powerhouse together with the generator and control equipment.
• After leaving the turbine, the water discharges down a ‘tailrace’ canal back into the river.
Hydro-scheme components
Weir and intake
Forebay tank
Penstock
Leat
Tailrace
Powerhouse
Spillway
2.4 Different site layouts
In practice, sites that are suitable for small-scale hydro schemes vary greatly. They include mountainous
locations where there are fast-flowing mountain streams and lowland areas with wide rivers. In some
cases development would involve the refurbishment of a historic water power site. In others it would
require an entirely new construction. This section illustrates the four most common layouts for a mini-
hydro scheme.

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A variation on the canal-and-penstock layout for medium and high-head schemes (Section 2.3) is to use
only a penstock, and omit the use of a canal. This would be applicable where the terrain would make
canal construction difficult, or in an environmentally-sensitive location where the scheme needs to be
hidden and a buried penstock is the only acceptable solution.
For low head schemes, there are two typical layouts. Where the project is a redevelopment of an old
scheme, there will often be a canal still in existence drawing water to an old powerhouse or watermill. It
may make sense to re-use this canal, although in some cases this may have been sized for a lower flow
than would be cost-effective for a new scheme. In this case, a barrage development may be possible on
the same site.
With a barrage development, the turbine(s) are constructed as part of the weir or immediately adjacent to
it, so that almost no approach canal or pipe-work is required.
A final option for the location of new mini-hydro turbines is on the exit flow from water-treatment plants
or sewage works. This application is growing in popularity with UK water companies.
Canal and Penstock Penstock Only
Mill Leat Barrage

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3. ESSENTIAL INFORMATION ABOUT YOUR SITE
3.1 Summary
There are a few pieces of essential information that need to be obtained when a new site is being
considered for hydro generation.
1. Firstly, one has to identify whether there is a significant energy resource. This involves estimating or
measuring the flow and available head, and estimating what annual energy capture would result.
2. If the potential output of a scheme is attractive, then one needs to be certain that permission will be
granted to use all of the land required both to develop the scheme and to have the necessary access to
it.
3. Finally, there needs to be a clear destination for the power: is there a nearby load that needs to be
supplied, or is there a convenient point of connection into the local distribution network?
These issues are explored in more detail below.
3.2 Flow
3.2.1 Obtaining Flow Data
The Environment Agency measures the flow in most significant rivers and streams in the UK, and data
from the 1300 gauging stations can be obtained from the Centre for Ecology and Hydrology in
Wallingford. Data for 200 sites is available over the internet, at: www.nwl.ac.uk/ih/nrfa/. These records
can be used to assess stream flow at the proposed site, as long as due allowance is made for the actual site
location in relation to the gauging station (upstream or downstream).
If no data is available, it is also possible to use hydrological methods that are based on long-term rainfall
and evaporation records, and on discharge records for similar catchment areas. This allows initial
conclusions to be drawn on the overall hydraulic potential without taking actual site observations. It is
advisable to follow this up with site measurements once the project looks likely to be feasible.
The reference books included in the bibliography offer a number of more or less sophisticated methods
both for estimating the hydrology of a catchment area and for measuring the flow in streams.
The most accurate and reliable flow measurement method is to install a measuring weir, as summarised
below.
3.2.2 Measuring weirs
A flow measurement weir has a rectangular notch in it through which all the water in the stream flows. It
is useful typically for flows in the region of 50-1000 l/s. The flow rate can be determined from a single
reading of the difference in height between the upstream water level and the bottom of the notch (see
Figure). For reliable results, the crest of the weir must be kept 'sharp' and sediment must be prevented
from accumulating behind the weir.
The formula for a rectangular notched weir is:
5.1
d h)h2.0L(g2C
3
2
Q −=
where:
Q = flow rate (m3
/s)
Cd = the coefficient of discharge
L = the notch width (m)

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h = the head difference (m)
g = acceleration due to gravity (9.81m/s2
)
If Cd is taken, typically, as 0.6, then the equation becomes:
Q = 1.8 (L - 0.2h) h1.5
Since stream flow varies both from day to day and with the season, measurements should ideally be taken
over a long period of time, preferably several years.
Measuring Weir
3.2.3 Flow Duration Curve
There are two ways of expressing the variation in river flow over the year: the annual hydrograph and the
Flow Duration Curve or FDC, as illustrated below.
The annual hydrograph is the easiest to understand, since it simply shows the day-by-day variation in
flow over a calendar year. However, the FDC is more useful when calculating the energy available for a
hydro-power scheme.
The FDC shows how flow is distributed over a period (usually a year). The vertical axis gives the flow,
the horizontal axis gives the percentage of the year that the flow exceeds the value given on the y-axis.
Hence, for example, the FDC can immediately indicate the level of flow which will be available for at
least 50% of the year (known as Q50). The flow exceeded for 95% of the year (Q95) is often taken as the
characteristic value for minimum river flow.
FDCs are often very similar for a region, but can be affected by soil conditions, vegetation cover, and to a
lesser extent by catchment shape. They are also modified by man-made reservoirs, abstractions and
discharges.
A flatter FDC (characterising a heavily spring-fed river) is preferable to a steeply sloping one, and means
that the total annual flow will be spread more evenly over the year, giving useful flow for a longer period,
and less severe floods.

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Compensation Flow
A portion of the flow, termed the compensation flow, will need to by-pass the scheme for environmental
or aesthetic reasons. In abstraction schemes, where water is diverted from the main course of the river,
this compensation flow is needed to maintain the ecology and aesthetic appearance of the river in the
depleted stretch.
The amount of compensation flow will depend on site-specific concerns, but a reasonable first estimate
will lie between the Q90 and Q99 values of river flow.
Annual Hydrograph Flow Duration Curve
3.3 Head
3.3.1 Head measurements
The head of water available at any one site can be determined by measuring the height difference between
the water surface at the proposed intake and the river level at the point where the water will be returned.
A number of reference books can provide details of basic survey techniques to measure or estimate the
available head. The most common methods are summarised as follows.
An initial estimate for a high-head site (> 50m) can be taken from a large-scale map, simply by counting
the contours between the inlet and discharge points: the distance between contours on standard Ordnance
Survey maps is 10 m.
Altimeters can also be useful for high-head pre-feasibility studies. Surveying altimeters in experienced
hands will give errors of as little as 3% in 100m. Atmospheric pressure variations need to be corrected
for, however, and this method cannot be generally recommended except for approximate readings.
The use of a Dumpy level (Theodolite or builder's
level) is the conventional method for measuring
head accurately and should be used wherever time
and funds allow. Such equipment should be used
by experienced operators who are capable of
checking the calibration of the device.

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Low-head schemes
An important factor on low head schemes is that the
gross head is not a constant but varies with the river
flow. As the river fills up, the tailwater level very
often rises faster than the headwater level, thus
reducing the total head available. To assess the
available gross head accurately, headwater and
tailwater levels need to be measured for the full
range of river flows.
3.4 Preliminary power and energy calculation
3.4.1 Design Flow
It is unlikely that schemes using significantly more than the mean river flow (Qmean) will be either
environmentally acceptable or economically attractive. Therefore the turbine design flow for a run-of-
river scheme (a scheme operating with no appreciable water storage) will not normally be greater than
Qmean. The exception would be a scheme specifically designed to capture very high winter flows, which is
very rare in mini-hydro applications.
The greater the chosen value of the design flow, the smaller proportion of the year that the system will be
operating on full power, i.e. it will have a lower ‘Capacity factor’.
3.4.2 Capacity Factor
The ‘Capacity factor’ is a ratio summarising how hard a turbine is working, expressed as follows:
Capacity factor (%) = Energy generated per year (kWh/year)
Installed capacity (kW) x 8760 hours/year
A first estimate of how Capacity factor varies with design flow is given as follows:
Design Flow Qo Capacity Factor
Qmean 40%
0.75 Qmean 50%
0.5 Qmean 60%
0.33 Qmean 70%
3.4.3 Rated Power
The peak power P can be estimated from the design flow Q0 and head H as follows:
P(kW) = 7 × Qo(m3
/s) × H(m)
3.4.4 Energy Output
The annual energy output is then estimated using the Capacity Factor (CF) as follows:
Energy (kWh/year) = P (kW) × CF × 8760

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There is clearly a balance to be struck between choosing a larger, more expensive turbine which takes a
high flow but operates at a low Capacity factor, and selecting a smaller turbine which will generate less
energy over the year, but will be working flat out for more of the time i.e. a higher Capacity factor. The
Capacity factor for most mini-hydro schemes would normally fall within the range 50% to 70% in order
to give a satisfactory return on the investment.
Most turbines can operate over a range of flows (typically down to 20-40% of their rated flow) in order to
increase their energy capture and sustain a reduced output during the drier months.
3.5 Use of the Land
No project can proceed unless you have the right to utilise all the land in question. It is also important to
establish how contractors will access the different parts of the scheme with the necessary equipment, and
to confirm that these routes will be available.
It is therefore wise to approach the relevant land-owners at an early stage to establish any objections to
the proposed scheme and to negotiate access. Since water courses often form property boundaries, the
ownership of the banks and existing structures may be complex. Failure to settle this issue at an early
stage may result in delays and cost penalties later in a project.
Leasing agreements will need to be drawn up which establish the right to use the necessary land areas and
also to define the responsibilities of the tenant in maintaining it. For example, the operator of a scheme
may be required to take on the maintenance liability of an existing weir and mill leat as part of the
agreement allowing him to install a turbine in the old mill.
3.6 Grid-connect or stand-alone
It is important to determine at the outset what the
value of the electricity generated by the scheme
will be, i.e. to whom the power will be sold.
The electricity generated by a scheme may be used
at the point of generation, in place of electricity
supplied by the local electricity company.
Alternatively it may be exported via the local
distribution network by agreement with the
Distribution Network Operator (DNO).
It is nearly always financially advantageous to
consume as much of the power as possible on site,
and only export the surplus into the network.
If the scheme is to produce power for export to the local network, there should be early discussions with
the DNO who will specify the system protection and metering equipment, and will also provide an
estimate of connection costs and the best location for feeding into their system.
A useful list of Distribution Network Operators is provided on the PV-UK website
(www.pv-uk.org/reference/grid-con/dno_contacts.html).

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4. COMMISSIONING A FEASIBILITY STUDY
4.1 Preliminaries
4.1.1 Getting Professional Help
Any developer should seek independent professional advice before committing significant finance to the
design and construction of a small-scale hydro scheme.
The involvement of professionals in a small-scale hydro development can range from preliminary site
assessment, through the conducting of a feasibility study, to a full ‘turnkey’ service, handling every
aspect of a development. In addition, there are several companies that lease, develop and operate sites as
a business activity, and can provide a full skills and finance package.
4.1.2 Preliminary Site Assessment
An experienced hydro professional should be able to indicate whether a site is worth considering further,
on the basis of an initial site visit and discussions with the developer and others. Preliminary
investigations of this type will typically require no more than 2-3 days’ work and will cost between £300
and £1000. A minor investment at this stage could save much greater expense and potential
complications later in the development process.
The main issues that should be considered in a preliminary investigation are:
• The existence of a suitable waterfall or weir and a turbine site
• A consistent flow of water at a usable head
• The likely acceptability of diverting water to a turbine
• Suitable site access for construction equipment
• A nearby demand for electricity, or the prospect of a grid connection at reasonable cost
• The social and environmental impact on the local area
• Land ownership and/or the prospect of securing or leasing land for the scheme at a reasonable cost
• An initial indication of design power and annual energy output
The accuracy of the information may only be plus or minus 25%, however, this should be sufficient for
deciding whether to proceed to a more detailed feasibility study.
4.2 Feasibility
A feasibility study uses accurate data and looks closely at costs. It can take the project forward from the
initial idea to a final design that will support applications for project finance and the necessary licenses. It
is therefore wise always to employ a professional to conduct the feasibility study and the detailed design
work.
The cost of a full feasibility study carried out by an independent consultant depends on its scope and on
the specific characteristics of the site, but would typically be £5,000-£10,000.
For a domestic-scale scheme (i.e. less than 30 kW), a detailed feasibility may not be affordable, and a less
detailed Pre-feasibility Study may prove sufficient. This would cover the same basic ground but use
approximate data analysed less extensively. It should be possible to commission a pre-feasibility study
for less than £3000.
The following essential tasks should form components of a feasibility study:

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1. Hydrological Survey. Typically, a hydrological survey would produce a flow duration curve. This
would be based on long-term records of rainfall and/or flow data, together with a knowledge of the
catchment geology and soil types. This long-term information might be backed up by short-term flow
measurements. The study should also include an estimate of the required compensation flow.
2. System design. This would include a description of the overall project layout, including a drawing
showing the general arrangement of the site. The prominent aspects of the works should be described
in detail, covering:
• Civil works (intake and weir, intake channel, penstock, turbine house, tailrace channel, site
access, construction details)
• The generating equipment (turbine, gearbox, generator, control system)
• Grid connection
3. System costing. A clear system costing would include a detailed estimate of the capital costs of the
project, subdivided into:
• Civil costs
• The cost of grid-connection
• The cost of electro-mechanical equipment
• Engineering and project management fees
4. Estimate of energy output and annual revenue. This would summarise the source data (river
flows, hydraulic losses, operating head, turbine efficiencies and methods of calculation) and calculate
the output of the scheme in terms of the maximum potential output power (in kW) and the average
annual energy yield (kWh/year) converted into annual revenue (£/year)
An additional task, which may form part of the main feasibility report but is often undertaken separately,
is the environmental assessment of the scheme, discussed in Section 4.3.
4.3 Environmental impact
4.3.1 The Environmental Statement.
Some form of environmental assessment is essential when it comes to applying for planning permission
and environmental licenses.
Under the Town and Country Planning (Assessment of Environmental Effects) Regulations 1988, the
planning application for any development that the planning authority considers likely to have a significant
impact on the environment must be accompanied by an Environmental Statement. This document
provides an assessment of the project’s likely environmental effects, together with any design,
construction, operational and decommissioning measures that are to be taken to minimise them. It would
typically cover such issues as flora, fauna, noise levels, traffic, land use, archaeology, recreation,
landscape, and air and water quality.
The Environment Agency may also require a report assessing the environmental effects of the
development. If the planning authority has asked for an Environmental Statement, this may meet the
requirements of the Environment Agency. However, the Environment Agency may ask for
environmental information even if the local planning authority does not. Such information might cover
water use, water quality, fisheries, river ecology, flood defence, nature conservation and public recreation
issues. The Environment Agency should be consulted at an early stage and will provide guidance on
what is required.
Specialist environmental consultants may be employed if project complexity merits their involvement.
However, general hydro consultants with an appropriate track record may also undertake an assessment of
this type.

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4.3.2 Fisheries
Hydro-installations on rivers populated by
migrating species of fish, such as salmon or trout,
are subject to special requirements as defined in the
Salmon and Freshwater Fisheries Act.
Migratory fish must not be ingested into the turbine
(so the mesh of the trashrack must be fine enough),
and there must be a water passage by-passing the
hydro-plant at all times so that fish can migrate up
or downstream. To allow fish to pass upstream
sometimes requires the construction of a 'fish
ladder', which is usually a series of pools one above
the other, with water overflowing from the higher
ones to the lower ones, so that fish can jump up
from one pool to the next.
5. PLANNING AND LICENSES
5.1 Whom to consult
Informal and formal consultation should underpin every stage of a development and may be handled
either by the developer or by a hydro professional. Consultation will be tailored to each individual
development. Some sites, for instance, may not be located on fishing rivers and therefore consultation
with fisheries bodies or angling clubs would be limited. Similarly, where a site does not require planning
permission, there is no need for detailed consultation with the relevant planning authorities.
The bodies listed in the table below should be approached, as appropriate, at the outset of a development,
and contact should be maintained throughout. Full consultation will ensure that any problems are
identified at an early stage, and this may prevent the incurring of unnecessary expenditure.
Body to be consulted Purpose of Consultation
The Environment Agency (England and
Wales)
Scottish Environmental Protection Agency
(SEPA)
To ensure that the site is acceptable
To establish a design that is acceptable
To identify the permissions required
To discuss and agree an acceptable river operating
regime (i.e. amount and timing of abstractions)
Relevant planning authority To ensure that the site is acceptable
To establish a design that is acceptable, especially
where construction work is needed
To identify permissions required
Fisheries bodies or those with an interest in
fisheries (e.g. angling clubs).
Scotland: the District Salmon Fisheries
Board
To address possible concerns at the design stage
Statutory environmental bodies e.g.
English nature and the Countryside
Commission; Scottish Natural Heritage
To address potential environmental impacts at the
design stage

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Body to be consulted Purpose of Consultation
Landowners To address ownership, access and leasing issues,
way-leaves for cables
To address possible objections to development
Regional Electricity Company (REC) If an electricity connection is required, to establish
any design constraints and connection costs
If appropriate, to enter negotiations for electricity
sale
5.2 Planning issues
Planning aspects of hydro developments are the responsibility of the local planning authority in England
and Wales. Planning permission will be required for most hydro developments. A possible exception is
the refurbishment of an existing scheme, where there is no ‘change of use’.
The planning department will indicate whether planning permission is required and also whether other
related procedures, such a Building Regulation Approval or the submission of an Environmental
Statement, are necessary.
As well as giving advice on how to make an application and on the fee charged, the planning department
will also suggest who should be consulted, indicate sensitivities to development, and outline measures
that might be taken to make developments more acceptable. An early approach to the planning
department is recommended so that any uncertainties can be clarified and a good working relationship
established.
The primary issues of concern to the planners are likely to be:
• The visual appearance of the scheme, including the powerhouse and penstock in particular
• Potential noise impacts on nearby residents
• Disturbance during the construction phase, both to local residents and disrupting traffic
• Preservation of structures of historical importance
On environmental issues, the planners will normally take advice from their statutory consultees, such as
the Environment Agency and English Nature. They will also be able to advise on whether the scheme
warrants a public display for the purpose of presenting the project to local people and helping allay any
concerns.
It is sometimes advisable to apply for outline planning permission in the first instance, in which the main
elements of the scheme can be agreed but without the completion of the final design. This means that the
overall planning process will be longer, but allows feedback received during the outline planning process
to be accommodated more easily into the final design and therefore reduces the risk of the full planning
application being rejected.
5.3 Environmental issues
5.3.1 Licences
All water courses of any size in England and Wales are controlled by the Environment Agency. To
remove water from them (even though it may go back in) will almost certainly require their permission in
the form of a licence. There are three licences that can apply to a hydropower scheme
• Abstraction Licence, if water is being diverted ‘away from the main line of flow of the river’. In
practice, this means that the only type of scheme which can avoid an abstraction licence would be a
barrage-type project where turbines are installed on an existing weir and the water remains between

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the existing banks of the river. All new abstraction licences are now time-limited to 12 years, after
which they must be renewed. The Environment Agency have stated that there will be a “presumption
of renewal”, but this is clearly an area of risk for new developments.
• Impoundment Licence, if changes are being made to structures which impound water, such as weirs
and sluices, or if new structures are to be built.
• Land Drainage Consent, for any works being carried out in a ‘main channel’
The Environment Agency may also require a Section 158 Agreement to be drawn up, which defines
certain further details on the way the scheme must be operated in order not to conflict with the Agency’s
river management duties, e.g. rights of access, the control of river levels, flood waters, maintenance of the
weir and river structures, etc..
5.3.2 Approaching the Environment Agency
Beyond the licensing procedures, the Environment Agency are also responsible for fish protection and
other environmental aspects of any riverside development. Whilst they have a duty to protect the
environment from harmful development, EA officers are generally sympathetic to green energy schemes.
They will also advise on the scope of any environmental assessment that may be needed.
The Environment Agency have published an
internal document ‘Hydropower – A handbook
for Agency Staff (May 2003)’ which lays out their
approach to assessing new schemes and which they
will provide on request to prospective developers.
That document advises that developers should:
• approach the Agency at an early stage and
maintain a dialogue with them
• respect the fact that the Agency cannot
compromise its statutory duties
• maintain a flexible approach to the proposed
scheme in respect of measures to mitigate its
impact, even where this may be at the expense
of some generating capacity.
[Available from: http://www.environment-agency.gov.uk/commondata/103599/hydropower_manual_e_882335.doc]
Schemes less than 500kW are not required by law to produce a formal Environmental Impact
Assessment. However, all license applications normally need to be supported by an Environmental Report
which summarises the details and impacts of the scheme. The Agency will provide the required scope of
such report during initial consultations – the main headings are contained in the Handbook mentioned
above.
6. COSTS AND ECONOMICS
6.1 Investment Costs
Small hydro costs can be split into four segments :
1. Machinery
This group includes the turbine, gearbox or drive belts, generator and the water inlet control valve.

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Generally speaking, machinery costs for high head schemes are lower than for low head schemes of
similar power. High head machines have to pass less water than low head machines for the same power
output and are therefore smaller. They also run faster and thus can be connected directly to the generator
without the complication of gearbox or belts.
2. Civil Works
This includes the intake, forebay tank and screen, the pipeline or channel to carry the water to the turbine,
the turbine house and machinery foundations, and the tailrace channel to return the water to the river.
The Civil Works are largely site-specific. On high head sites the major cost will be the pipeline; on low
head sites probably the water intake, screens and channel.
3. Electrical Works
The electrical system will involve the control panel and control system, the wiring within the turbine
house, and a transformer if required, plus the cost of connection to the electricity. These costs are largely
dependent on the maximum power output of the installation. The connection cost is set by the local
electricity distribution company.
4. External Costs
This could encompass the engineering services of a professional to design and manage the installation,
plus the costs of obtaining a the licences, planning permission, etc.
For a 100kW small hydro installation, the costs could range as follows:-
Low head High head
£1000s £1000s
Machinery 60 – 120 30 - 60
Civil works 30 – 100 30 - 80
Electrical works (no grid connection) 15 - 30 15 - 30
External costs 10 - 30 10 - 30
Total: 115 – 280 85 – 200
Generally, the cost per kilowatt of new schemes increases as size reduces, due to economy of scale and
the fact that any scheme has a certain fixed cost element which does not greatly change with size of
scheme.
6.2 Running Costs
6.2.1 Leasing
If part of the land is leased, then there will be an annual rent to pay. It can be beneficial to tie this rent
into the revenue from the scheme, so that the landlord also has an incentive for the turbines to be
operating. Schemes which lease all the land should expect to pay no more than 4% of annual revenue as
rent, and the lower you can negotiate the better!
6.2.2 Metering
Larger schemes currently require half-hourly metering to be installed, which has to be monitored by an
independent meter-reading company, although this requirement may change in the future. There is an
annual charge to pay for this service, currently in the range £350 - £1000 / year.
6.2.3 Rates
Hydroelectric schemes are subject to business rates unless they are seen as being part of a domestic
property. The rateable value is constantly under review, and the correct value for 2004 was £9 per kW
installed which, when multiplied by the Unified Business Rate (0.46 in 2004), gives the annual sum to be
paid.

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6.2.4 Maintenance and Servicing
Modern, automated equipment requires very little maintenance. The cost of routine inspections and an
annual service should come to no more than 1-2% of the capital cost of the scheme. As the machine ages,
there will eventually be extra costs associated with replacing seals and bearings, a new generator,
refurbished sluice gates, etc., but these should not occur for at least 10 years.
6.2.5 Insurance
Although hydro plant is generally very reliable, the following insurances are recommended (and may be
required by financiers):
• Material damage insurance against the cost of repairing damage to the works caused by fire and
‘special perils’ such as explosions, storms, flooding, impact and malicious damage
• Business interruption insurance against profit loss caused by fire or special perils damage
• Public and employer’s liability insurances, which are required by law; a minimum indemnity of £5
million is recommended.
6.3 Maximising the revenue from your scheme
Operators of ‘clean’ electricity plant can generate revenue by selling:
• The electricity itself
• Renewable Obligation Certificates
• Levy Exemption Certificates
If the electricity generated by a hydro-scheme is sold directly to an electricity company, then the price
offered for the electricity itself is relatively small - in the range 2.0 – 3.0 p/kWh on average over the year.
Alternatively, if there is a substantial electrical load close to where the power is being generated (e.g.
factory or office complex), it will be more beneficial to use the hydropower to feed that load, so
displacing electricity that would otherwise be bought in from the grid at perhaps 3.5 – 5.5 p/kWh.
For smaller schemes, some electricity companies are willing to enter into a special contract which will
balance the energy generated against the energy consumed on site on an annual or quarterly basis.
Furthermore, business customers who would otherwise have to pay an extra 0.43 p/kWh for the Climate
Change Levy will make that additional saving on any hydroelectricity they buy from the scheme.
ROCs
Electricity generated from renewable sources can be used to obtain Renewables Obligation Certificates
(ROCs) which all the supply companies need in order to prove they are meeting the governments targets
for renewable energy. ROCs have a market value in the range 3p – 4.5p per kWh which will vary over
time depending on how well these companies are doing in meeting their targets. The concept and trading
of ROCs is illustrated below.
Levy Exemption Certificates (LECs)
Green electricity which is sold into the grid will generate Levy Exemption Certificates (LECs) which can
be sold on to business customers to enable them to avoid paying the full Climate Change Levy. The
LECs can be sold for up to 90% of the Levy value.
Electricity Traders
There are several options on who to approach to obtain the maximum income for your scheme. Not only
will any one of the main electricity supply companies (Powergen, npower, etc.) make an offer for your
output (including the ROCs, LECs, etc.), it is also possible to approach a range of specialist electricity
trading companies which focus purely on getting the best price for renewable energy schemes. The BHA
will be able to advise on which companies are offering the best deal for mini-hydro generation.

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Ofgem issues ROCs to all registered generators of green electricity. They can sell them either to ROC traders or
directly to the electricity supply companies who need them to meet their Renewable Energy Quota.
6.4 Financial Assistance
The government has introduced a range of incentives to encourage investment in mini-hydro schemes and
renewable energy in general.
6.4.1 Tax breaks
• For domestic developers and other non-commercial owners, the government has reduced the VAT
payable on hydro-electric plant to 5% for systems supplying buildings which are either residential or
used for charitable purposes.
Since many components of a hydro-scheme are not obviously “hydro-electric plant” on their own, the
best advantage of this tax-break will be obtained by requesting a hydro installer to procure all
hardware for the scheme which he can then genuinely pass on as part-and-parcel of the overall hydro-
plant.
6.4.2 Grants
• The government’s Clear Skies initiative for England and Wales offers grants to domestic owners of
mini-hydro plant equal to £1000 per kW installed, up to a maximum of £5000. The equipment must
be chosen from an approved product list, and installed by a registered installer. Further details on
www.clear-skies.org.uk
• Clear Skies offers larger grants to “community” schemes which are owned and operated by a non-
profit organisation to the benefit of the local community. Such organisations can include councils,
schools, housing associations, etc. A grant of up to 50% of project costs can be obtained up to a
maximum of £100,000. An essential element of these schemes is their ability to raise awareness
within the community and improve the national profile of renewable energy schemes.
• In Scotland, the Community and Household Renewables Initiative (SCHRI) offers grants on a similar
basis to Clear Skies.
• There are a wide range of regional funding mechanisms which can offer grants towards small-scale
renewable energy projects. District and County Councils should be able to advise on the availability
of such funds.

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7. CONTRACTING A SCHEME
7.1 Development Options
7.1.1 Turnkey Contracts
Since any hydro scheme requires a substantial up-front investment, it is clearly essential that the project is
implemented correctly and with robust engineering and equipment.
For the larger schemes, requiring a few hundreds of thousands of pounds investment, it will be important
for the project to be managed by a professional hydro-engineering firm, and installed by an experienced
contractor.
The most common approach for implementing larger projects is the “turnkey contract” in which a single
contractor takes on the entire scheme from start to finish. The contractor, who might be a civil
engineering company or the turbine supplier, brings together a team of sub-contractors and suppliers
under a single contract, typically following a competitive tendering process.
From the owner’s point of view, this greatly simplifies the management of the job. However, since the
main contractor is taking on most of the risks and unknowns, this will inevitably be reflected in the cost
of the tender.
7.1.2 DIY
For the smaller schemes (generally less than 50 kW), it may be possible for the owner and his local team
of contractors to share the tasks of implementing the scheme with the equipment supplier.
This approach can lead to significant savings on the project cost, but requires the responsibilities of the
different parties to be very clearly defined.
Even if the owner is keen to adopt a DIY approach, there are certain activities where professional inputs
will be essential to ensure the technical viability of the scheme. These areas can be summarised as
follows:
1. The detailed site survey
2. The general layout of the scheme
3. The design of the intake
4. The layout of the powerhouse
5. The specification of the turbine and penstock
6. The installation and commissioning of the electro-mechanical equipment (which would normally
be undertaken by the turbine supplier)
Therefore the main tasks which the scheme-owner may feel he can implement using local labour would
be:
1. Construction of the intake works
2. Installation of the penstock pipe
3. Construction of the powerhouse and tailrace
4. Laying of electrical cabling
All of the above would be completed to a specification provided by the equipment supplier or hydro-
power consultant.
7.2 Suppliers
Small-scale hydro power is a proven and mature technology. Reliable and efficient equipment and sound
advice is available from a range of experienced suppliers and manufacturers in the UK and worldwide.

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The term ‘supplier’ covers any company which will sell you equipment for your scheme. They may also
be the manufacturer, or they may be the agent for imported equipment.
Many turbine manufacturers will also offer to supply the full equipment package including the gearbox,
generator, control panel, trashrack, sluice gate, etc. which they will assemble from their preferred sub-
contractors.
The BHA maintains a database of UK equipment suppliers. Other useful web-sites for locating national
and international suppliers are:
The International Journal of Hydropower and Dams
(http://www.hydropower-dams.com/atlas/industry.html)
James and James Publishers
(http://www.jxj.com/suppands/renenerg/index.html)
Suppliers are usually willing to provide a ‘budget quote’ for the equipment for your scheme, based on
limited information, in order to help you identify whether their equipment is appropriate and affordable
without wasting excessive effort.
The minimum information they would need to respond to an enquiry would be the design head and flow.
Additional useful information to include in such a request would be:
• Scheme location
• Length and diameter of penstock
• Flow Duration Curve and compensation flow
• Type of turbine required (if already known)
• Any unusual constraints of the site e.g. environmental sensitivities
The typical lead time for a turbine, from placing an order to delivery on site, is between 5 and 9 months.
This is an important consideration when planning the timescale of a development.
7.3 Installers
Installers are engineering companies who will manage the specification, procurement, installation and
commissioning of all the components of a hydro-scheme. In essence, they will offer a turnkey project for
the electro-mechanical aspects of the scheme. Most installers would also offer to undertake the site survey
and initial feasibility work.
Some installers may also take on the civil works, if relatively minor, otherwise a civil contractor will also
be required to implement work to the installer’s specification.
The government’s Clear Skies programme operates a list of registered UK installers who may be used to
install equipment receiving a Clear Skies grant. The list is available from: www.clear-skies.org.uk
The most reliable method for checking an installer’s credentials is to obtain references from previous
work. Installers should be able to supply a list of past projects and the contact details of at least one
recent customer. The BHA will be able to confirm whether an installer is a member of the Association
and has a known track record in the industry.

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7.4 Commissioning and handover
The final stage in the installation of a micro-hydro plant involves performance tests. The purpose is to
check the function of the different components of the scheme and to measure the overall system
performance against the figures arrived at during the design of the scheme.
Depending on the complexity of the system, it may take several months before all working conditions are
experienced. Hence, although formal commissioning and hand-over may be completed in a few days, the
end-user should not consider the job fully completed until satisfied that all operating conditions have been
met.
Important activities during commissioning will include:
• Ensuring sufficient flow is being drawn through the intake
• Confirming that the channel can pass the design flow without undue head loss
• Checking that surplus water passing through the intake will escape down the appropriate
spillways and will never overflow the channel walls
• Confirming that the design flow will pass down the penstock without entraining air at the forebay
• Measuring the head loss in the penstock
• Checking the penstock joints for leaks
• Confirming the smooth running of the turbine and generator, including checking the bearings for
noise and temperature
• Checking that belts and pulleys are correctly aligned, or that the gearbox is operating effectively
without overheating
• Ensuring that the lubricating systems are working for the bearings and gearbox
• Confirming that the turbine achieves its design power at rated head and flow
• Checking all the functions of the control panel, in particular start-up and shut-down sequences
plus all the switchgear which interface and protect the system from the grid
7.5 Operating the scheme
Both the lifetime of the equipment and the level of effort required for operation and maintenance will
depend on the project design, although small-scale hydro schemes tend to have long lifetimes and low
maintenance costs.
Modern schemes are usually automated, and regular maintenance is restricted to tasks such as the
occasional clearing of the intake trash-rack and the greasing of parts of the generating equipment. Older
schemes may require more regular manual intervention, for instance to operate sluice gates or control
valves. In some cases, remote monitoring can be used to give an early indication of faults.
During system commissioning, the installer should run through all the routine inspection and maintenance
tasks with the owner of the scheme. He will also provide the documentation from the various equipment
suppliers which should detail the relevant maintenance tasks and timings for each part of the system.
If the electro-mechanical equipment is of modern design, only an annual service will be necessary. This
can usually be carried out during the summer low-flow period when the plant is unlikely to be generating.
It will typically be undertaken by the equipment supplier or the installer and will take about two days.
8. TECHNOLOGY
8.1 Overview
All hydro turbines convert the energy from falling water into rotating shaft power, but there is often
confusion as to which type of turbine should be used in different circumstances.

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The selection of the turbine depends upon the site characteristics, principally the head and flow available,
plus the desired running speed of the generator and whether the turbine will be expected to operate in
reduced flow conditions.
8.1.1 Classification
Turbines can be crudely classified as high-head, medium-head, or low-head machines, as shown in Table
1.
Electricity generation usually requires a shaft speed as close as possible to 1500rpm to minimize the
speed change between the turbine and the generator. Since the speed of any given type of turbine declines
with head, low-head sites need turbines that are inherently faster under a given operating condition.
Turbines are also divided by their principle of operation and can be either impulse or reaction turbines.
The rotor of the reaction turbine is fully immersed in water and is enclosed in a pressure casing. The
runner blades are profiled so that pressure differences across them impose lift forces, just as on aircraft
wings, which cause the runner to rotate.
In contrast an impulse turbine runner operates in air, driven by a jet (or jets) of water.
There are 3 main types of impulse turbine in use: the Pelton, the Turgo, and the Crossflow (or Banki)
turbines. The two main types of reaction turbine are the propeller (with Kaplan variant) and Francis
turbines.
The approximate ranges of head, flow and power applicable to the different turbine types are summarised
in the chart of Figure 1 (up to 500kW power). These are approximate and depend on the precise design of
each manufacturer.
Table 1 Impulse and Reaction Turbines
Turbine Type Head Classification
High (>50m) Medium (10-50m) Low (<10m)
Impulse Pelton Crossflow Crossflow
Turgo Turgo
Multi-jet Pelton Multi-jet Pelton
Francis (open-flume)
Reaction Francis (spiral case) Propeller
Kaplan
Figure 1 Head-flow ranges of small hydro turbines

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8.2 Types of turbine
8.2.1 Impulse Turbines
The Pelton Turbine consists of a wheel with a series of split buckets set around its rim; a high velocity jet
of water is directed tangentially at the wheel. The jet hits each bucket and is split in half, so that each half
is turned and deflected back almost through 180º. Nearly all the energy of the water goes into propelling
the bucket and the deflected water falls into a discharge channel below.
The Turgo turbine is similar to the Pelton but the jet strikes the plane of the runner at an angle (typically
20°) so that the water enters the runner on one side and exits on the other. Therefore the flow rate is not
limited by the discharged fluid interfering with the incoming jet (as is the case with Pelton turbines). As a
consequence, a Turgo turbine can have a smaller diameter runner than a Pelton for an equivalent power.
The Crossflow turbine has a drum-like rotor with a solid disk at each end and gutter-shaped “slats”
joining the two disks. A jet of water enters the top of the rotor through the curved blades, emerging on
the far side of the rotor by passing through the blades a 2nd
time. The shape of the blades is such that on
each passage through the periphery of the rotor the water transfers some of its momentum, before falling
away with little residual energy.
8.2.2 Reaction Turbines
Reaction turbines exploit the oncoming flow of water to generate hydrodynamic lift forces to propel the
runner blades. They are distinguished from the impulse type by having a runner that always functions
within a completely water-filled casing.
All reaction turbines have a diffuser known as a ‘draft tube’ below the runner through which the water
discharges. The draft tube slows the discharged water and reduces the static pressure below the runner
and thereby increases the effective head.
Propeller-type turbines are similar in principle to the propeller of a ship, but operating in reversed mode.
Various configurations of propeller turbine exist; a key feature is that for good efficiency the water needs
to be given some swirl before entering the turbine runner. With good design, the swirl is absorbed by the
runner and the water that emerges flows straight into the draft tube. Methods for adding inlet swirl
include the use of a set of guide vanes mounted upstream of the runner with water spiralling into the
runner through them. Another method is to form a “snail shell” housing for the runner in which the water
enters tangentially and is forced to spiral in to the runner.
When guide vanes are used, these are often adjustable so as to vary the flow admitted to the runner. In
some cases the blades of the runner can also be adjusted, in which case the turbine is called a Kaplan.
The mechanics for adjusting turbine blades and guide vanes can be costly and tend to be more affordable
for large systems, but can greatly improve efficiency over a wide range of flows.
The Francis turbine is essentially a modified form of propeller turbine in which water flows radially
inwards into the runner and is turned to emerge axially. For medium-head schemes, the runner is most
commonly mounted in a spiral casing with internal adjustable guide vanes.
Since the cross-flow turbine is now a less costly (though less efficient)alternative to the spiral-case
Francis, it is rare for these turbines to be used on sites of less than 100 kW output.
The Francis turbine was originally designed as a low-head machine, installed in an open chamber without
a spiral casing. Thousands of such machines were installed in the UK and the rest of Europe from the
1920s to the 1960s. Although an efficient turbine, it was eventually superseded by the propeller turbine
which is more compact and faster-running for the same head and flow conditions. However, many of
these ‘open-flume’ Francis turbines are still in place, hence this technology is still relevant for
refurbishment schemes.

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8.3 Turbine efficiency
8.3.1 Relative efficiencies
A significant factor in the comparison of different turbine types is their relative efficiencies both at their
design point and at reduced flows. Typical efficiency curves are shown in Figure 3.
An important point to note is that the Pelton and Kaplan turbines retain very high efficiencies when
running below design flow; in contrast the efficiency of the Crossflow and Francis turbines falls away
more sharply if run at below half their normal flow. Most fixed-pitch propeller turbines perform poorly
except above 80% of full flow.
Figure 3 Part-flow efficiencies
0
10
20
30
40
50
60
70
80
90
100
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
Q/Qo
Efficiency(%)
Full Kaplan
Pelton
Francis
Crossflow
Fixed propeller
8.4 Control
The control panel is the black box which monitors the
operation of the hydro scheme. The main functions of
the control panel are to:
• Start up and shut down the turbine
• Synchronise the generator with the local network
• Monitor the upstream water level and ensure it is
maintained above its minimum value
• Operate the flow-control valve to the turbine to
match the availability of water
• Detect faults and activate warning or shut-down
sequences
For grid-connected schemes, the control panel must conform to the G59 recommendations for the
connection of embedded generators. However, very small plant, less than 3.7 kW per phase, only needs
to comply with a reduced set of standards defined by the new G83 recommendations.
For schemes which are not connected to the local network, but operate in isolation, the control system
will ensure that both the voltage and frequency of the generator remain within the allowable ranges
regardless of the load being applied.
On larger plants supplying three phase power, it is usual for the control panel to have the following
displays:
• a voltmeter with a selector switch to read the voltage between phases and the line voltage,

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• an ammeter on each phase to measure current
• a frequency meter
• a kilowatt meter, for the instantaneous power
• a kilowatt-hour meter, for the energy generated over a period
• a power factor meter
8.5 Screening
8.5.1 Trash screens
The screen, or ‘trashrack’ filters out river-borne debris before
it reaches the turbine. It is an extremely important
component of the whole scheme, and can be one of the more
expensive items. The large majority of operating problems
and maintenance costs can be traced back to the screening
system so investment in a robust design will pay for itself in
the long run.
The first line of protection should, in most cases, be a
floating boom angled across the flow upstream of the intake.
This will catch large items of floating debris before they
reach the trashrack. However such debris will eventually
make it under the boom unless cleared within a few days.
The standard screening solution, which has been used since
the days of waterwheels, is to place a rack of bars in front of
the intake, with the bars spaced so that a rake can be used to
drag the accumulated debris up to the top of the screen.
The screen is a hindrance to the flow and introduces a slight head loss. Therefore the bar-spacing should
be the maximum that will still trap debris large enough to damage the turbine. The turbine supplier will
advise on the correct dimensions.
In addition, the flow velocity approaching the screen should be relatively slow, preferably less than
0.3 m/sec and certainly no greater than 0.5 m/sec.
8.5.2 Automatic cleaners
Manual raking is only viable for small schemes, or sites which are manned for other reasons. There are
now a range of automatic raking devices available to clean the screen and dispose of the trapped debris.
The most common types are:
A robotic rake. These come in a variety of designs, but usually involve one or more rakes operated by a
hydraulic ram. Some designs require only a single rake which can index along the screen; otherwise two
or more rakes can operate side by side. These systems are usually very robust, partly because they can
keep their drive mechanisms out of the water at all times. Their main disadvantages are the visual
presence of the equipment and the slightly greater health and safety risk posed by unattended operation of
the equipment.
A rake-and-chain cleaner, in which a bar is moved up the screen by a chain drive at each end. The bar
deposits the collected debris in a channel running the length of the screen. The channel can be flushed
clean by a water supply (pumped if necessary), washing the debris towards a side spillway.
The grab-and-lift cleaner is a robust alternative to the robotic rake. A single set of ‘jaws’ indexes along
the screen and lifts the material straight into a skip.

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Coanda screens, applicable only for high and medium head schemes, require no raking because they
utilise the Coanda Effect to filter out and flush away debris and silt particles, allowing only clean water
into the intake system. Precisely positioned, finely spaced horizontal stainless steel wires are built into a
carefully profiled screen which is mounted on the downstream face of the intake weir. Clean water is
collected in a chamber below the screens, which is connected directly to the turbine penstock.
(a) Rake and chain (b) Hydraulic arm
(c) Grab-and-Lift (d) Coanda screen
8.5.3 Fish-screening
On rivers where there are important fisheries concerns, the Environment Agency will stipulate more
stringent screening requirements to ensure that fish will be deterred from the turbine intake and will be
diverted to a suitable by-wash. The precise fish-screening measures will be a matter for negotiation,
depending on the sensitivities of the site.
Where there are salmon smolts migrating down-
river, it is normal for a mesh-spacing no greater
than 12 mm to be required for at least three months
in the spring and early summer. A fine-meshed
screen will accumulate large volumes of debris and
an automatic cleaner then becomes essential to
keep the turbine running.
A number of innovative methods for excluding fish
from intakes which avoid a physical screen are
being trialled. These include the use of electric
currents, bubble curtains and sound waves to guide
the fish away from the intake. These methods offer
significant advantages to the operator by avoiding
any obstruction to the flow, but are yet to find
general acceptance with the Environment Agency.
The Bio-Acoustic Fish Fence (BAFF) uses a combination of air
bubbles and sound waves to form a behavioural screen to guide
fish away from hydro intakes.

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9. FURTHER INFORMATION AND ASSISTANCE
9.1 The BHA
The British Hydropower Association (BHA) represents the interests of all those involved in the UK
hydropower industry. It promotes the use and awareness of small hydropower, and lobbies to protect its
members' interests. Regular newsletters keep readers updated on the hydropower industry in Britain.
Membership of the Association is open to any organisation or individual with an interest in the use of
waterpower. Members include manufacturers of all kinds of equipment used in the industry, civil,
mechanical and electrical consulting engineers, utility companies, academic institutions, developers -
large and small, individuals, charities and students - anyone who is interested in and keen to promote the
use of hydropower.
9.2 Reference books
There are very few books that have focused on the issues relating specifically to small-scale hydropower;
the most useful sources of information are listed below.
Readers looking for the hydraulic theory of turbines should examine traditional hydraulics engineering
textbooks; although these are usually written with large-scale projects in mind, the basic theory for a
small turbine is no different to that of a large turbine.
1. Micro-Hydro Design Manual, A.Harvey et al., IT Publications Ltd, London 1993.
A comprehensive technical guide to small-scale hydropower projects, focusing mainly on projects
<500kW. It covers the whole topic from initial site survey, through to equipment selection and
installation.
2. Micro-Hydro Power: a guide for development workers, P.Fraenkel, O.Paish, V.Bokalders,
A.Harvey, A.Brown, R.Edwards, IT Publications Ltd, London 1991 (reprinted 2001).
A shorter manual covering all the important topics but without going into in-depth technicalities.
3. Layman’s guidebook on how to develop a small hydro site. Published by the European
Commission, 200 Rue de la Loi, B-1049 Brussels, Belgium, 1994 (out of print but available by
download from www.esha.be).
This two-volume manual describes the principal steps to be taken in the development of a small hydro
site in Europe.
4. Hydropower – A handbook for Agency Staff. Environment Agency, May 2003
5. A UK Guide to Intake Fish Screening Legislation, Policy and Best Practice, Fawley Aquatic,
Crown Copyright, Department of Trade and Industry, 1998.
6. The Micro-hydro Pelton Turbine Manual, J Thake, ITDG Publishing, 2000.
9.3 Internet Links
Web-site for the British Hydropower Association:
http://www.british-hydro.org/
Web-site for the European Small Hydropower Association, including download of their Layman’s Guide
to small hydro:
http://www.esha.be/
Internet portal for micro-hydro power, with a focus on developing countries:
http://microhydropower.net
The National River Flow Archive, containing river flow data from the UK network of over 1300 gauging
stations:
www.nwl.ac.uk/ih/nrfa/

31.
British Hydropower Association A GUIDE TO UK MINI-HYDRO DEVELOPMENTS
O/MINI HYDRO WEB GUIDE - Download v1.2 29 21/06/06
An international hydropower industry guide as compiled by The International Journal of Hydropower and
Dams – mainly oriented towards larger companies and projects.
http://www.hydropower-dams.com/atlas/industry.html
The James & James database of Renewable Energy Suppliers and Services, holding the details of nearly
12,000 renewable energy companies and organisations from around the world.
http://www.jxj.com/suppands/renenerg/index.html
9.4 Terminology
Abstraction Licence Authorisation granted by the Environment Agency to allow the removal of water
from a source (permanently or temporarily)
Capacity factor
(also called ‘Load Factor’)
The ratio of energy output per year to the maximum output if the system runs at full
rated capacity all year round.
Compensation Flow The flow which must be left in the river at the point of abstraction, for ecological
purposes.
Fish Ladder (or Fish Pass) A structure consisting of a series of overflow weirs which are arranged in steps that
rise about 30cms in 3 to 4m horizontally, and serve as a means for allowing
migrant fish to travel upstream past a dam or weir.
Flow Duration Curve A graph showing the percentage of time that the flow at a particular gauging
station equals or exceeds certain values.
Forebay An open tank for slowing down the incoming flow and settling out silt and gravel
before the flow passes into the penstock.
Gauging Station A site where the flow of a river is measured.
Gross Head The difference between the upstream and downstream water levels.
Headrace The channel that forms the inlet to a turbine.
Impoundment Licence The authorisation granted by the Environment Agency to allow the obstruction or
impeding the flow of water.
Installed Capacity The total maximum output (kW) of the generating units in a hydropower plant.
Kilowatt (kW) Unit of power, equal to 1000 watts
Kilowatt hour (kWh) Unit of electrical energy, equal to the electricity supplied by 1 kW working for 1
hour. 1 kWh = 3,600,000 Joules
Leat or Lade An open channel that conveys water at a shallow gradient from a river channel
where sufficient head has been gained for a turbine to be installed. (Also
sometimes called Goit or Contour Canal).
Net Head The pressure head available to the turbine after friction losses through the intake
and trash rack.
Output The amount of power (or energy depending on definition) delivered from a piece of
equipment, station or system.
Penstock A pipe (usually steel, concrete or plastic) that conveys water under pressure from
intake to turbine.
Sluice Gates A vertical shaft slide gate, which can be operated either manually or by electric
motors (there are other types).
Spillway A controlled discharge of excess flow back into the river.
Tailrace The channel that takes flow away from the turbine outlet
Trashrack A protective screen that prevents large branches, tree trunks and other debris from
entering and damaging the turbine. It usually consists of vertical bars spaced
between 30-100 mm apart. The screen is typically cleaned by an automatic rake
which removes the debris, either to a platform or to be flushed into the river.
Turbine A machine converting the speed and/or pressure of flowing water into rotational
energy.
Weir A low dam which is designed to provide sufficient upstream depth for a water
intake while allowing flow to pass over its crest.